As is well-known, trucks having fully enclosed cargo space within the truck body are provided with a lighting system to facilitate loading and unloading of the cargo. Typically, the truck body, especially long haul trucks, is long relative to its height and width to provide the desired cargo capacity. The longstanding practice in lighting the interior of the truck body has been to use a plurality of incandescent lamps mounted in the roof of the truck body and spaced from each other from front to rear. Typically, the lighting fixtures comprise a lamp housing recessed into the roof and enclosing an incandescent lamp and having a light distributing lens disposed on the housing between the housing and the cargo space so it is generally flush with the interior surface of the roof. This arrangement provides the required illumination without the light fixture intruding into the cargo space.
The conventional incandescent lighting system described above has been found to be unsatisfactory because it is wasteful of energy, requires ongoing maintenance and it is sometimes used in such a manner that it constitutes a fire hazard. In refrigerated trucks, i.e. those which have a refrigeration system for the cargo space, the heat generated by the incandescent lamps is largely dissipated into the refrigerated cargo space thus requiring more energy for refrigeration. Also, it is known that some truck drivers like to increase the illumination in the cargo space by replacing the standard low wattage incandescent lamps with higher wattage with the result of increased heat generation and shortened life of the bulbs. This practice adds to the cost of bulb replacement in the maintenance of the lighting system. Additionally, the conventional incandescent lighting system constitutes a fire hazard, especially when the truck body is loaded with cargo close to the incandescent lamp fixtures and the lights are inadvertently left on for a long time. Such conditions can cause truck fires which are not only dangerous to life and limb but also constitute increased costs to the trucking industry by reason of loss and increased insurance premiums.
There has been a longstanding need in the trucking industry for a safe, effective and energy efficient lighting system for the cargo space in a container body of a truck.
In the prior art, certain fiber optic or "light pipe" systems have been proposed for use on vehicles. The Johnson et al. patent U.S. Pat. No. 4,947,293 granted Aug. 7, 1990 discloses a clearance lighting system for a semi trailer cargo container body. The lighting system includes a core light conducting material in the form of an elongated light conducting strip provided with a cladding material to provide a light guide. The core and cladding are constructed to provide lateral light emission as well as longitudinal propagation. A light source is adapted to end-illuminate the light guides for both sides of a container body from a single light source. A similar system which also provides a message panel is disclosed in Johnson patent U.S. Pat. No. 5,122,933 granted Jun. 16, 1992.
The Moore et al. patent U.S. Pat. No. 4,740,870 granted Apr. 26, 1988 describes a fiber optic lighting system for boats. In this system, a plurality of fiber optic cables extend from a central light source to respective plurality of remote light fixtures to provide lighting at different locations on the boat.
The Davenport et al. patent U.S. Pat. No. 4,811,172 granted Mar. 7, 1989 describes an optical fiber lighting system particularly suited for automobiles and air craft. The lighting system comprises subsystems suitable for high and low beam illumination and rear illumination of an automobile. Each subsystem comprises a high intensity light source coupled to one end of each of a plurality of light pipes with each having their other end positioned relative to a reflective element and a lens. The reflective elements are arranged to provide a prescribed illumination pattern.
The Finch et al. patent U.S. Pat. No. 5,184,883 granted Feb. 9, 1993 discloses an automobile lighting system similar to that described in the above-referenced Davenport patent U.S. Pat. No. 4,811,172. The Finch et al. patent describes an indicating device that comprises a shutter having an opaque portion, a light blocking position in which the opaque portion blocks the passage of light from the output end of a light guide to a lens and a non-blocking position in which light is allowed to pass through the indicating device to the lens.
A general object of this invention is to provide an improved lighting system for the cargo space of a truck which overcomes certain disadvantages of the prior art.